Interlocking electrical connectors and plugs having improved keying means



Aug. 29, 1967 E. R. cA SON 3,339,171 INTERLOCKING E J TRI I C ECIORS AND PLU HAVING PROVED K NG MEANS 2 Sheets-Sheet 1 GS Filed April 8, 1965 INVENTOR.

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z 0 W w A V 1 m W 4 6 M a u/MM w 1 11. 6 0 4 .T v /w 2 v H fl\ m /A Z M 6 IIH 4 1 fa x I m Z w 9 W MM w w W United States Patent 3,339,171 INTERLOCKING ELECTRICAL CONNECTORS This invention relates to electrical connectors and cooperating plugs having improved selective key means.

As is well known to those skilled in the electrical wiring device art, there are presently available various types of electrical wiring devices which have elements arranged to physically interlock with one another after mating to avoid accidental separation. One device of this type, which may be referred to as the post type, is disclosed in United States Patent No. 2,102,625, issued Dec. 21, 1937, to Harvey Hubbell, Jr. and assigned to the assignee of this application. The connector portion disclosed therein defines a socket containing female electrical contacts which is normally closed by a spring biased insulating closure plunger. The plug portion includes a central post which is formed from an electrical insulating material and carries the male contacts. When the plug is advanced into the socket, the post retracts the plunger inwardly and electrical engagement is made between the contacts. When fully inserted, the plug is rotated relative to the connector to physically lock the connector elements together.

Another well known type of interlocking electrical wiring device, which may be referred to as the blade type is disclosed in United States Patent No. 1,771,729, issued July 29, 1930, to Harvey Hubbell, Jr. and assigned to the assignee of this application. This type wiring device utilizes a connector having a front face defining a plurality of concentrically arranged arcuate slots leading to female contacts. The plug includes a plurality of curved contact blades arranged to enter the slots, and at least some of the blades include circumferentially extending locking shoulders. After the plug blades are inserted into the connector, the plug is rotated, causing the blades to slide within the arcuate slots until their shoulders engage the back surface of the front wall of the connector to lock the connection.

In order to increase the safety and versatility of interlocking electrical wiring devices, it has been proposed to provide them with keying means so that plugs of certain voltage and current ratings can be interconnected only with connectors of similar rating. United States Patents Nos. 3,023,394 and 3,120,985, of Harvey Hubbell,

assigned to the assignee of the instant invention, disclose interlocking blade type wiring devices having keying means. In each arrangement, a shaped key extends outwardly from the plug at approximately the center of the concentrically arranged male contact blades. The connector defines a key opening centrally positioned relative to its arcuate slots and shaped to receive the key. In order to provide for the necessary interlocking rotation between the plug and connector, two different approaches have been utilized. In US. Patent No. 3,023,394, for example, the key on the plug is fixed, and the key opening in the connector is defined by a rotatable insert. In US. Patent No. 3,120,985, the key is rotatably mounted on the plug, while the key opening is fixed in the connector.

Selective keying has also been adapted to wiring devices of the post type. For example, in United States patent application Ser. No. 411,831, filed Nov. 17, 1964,

- by James A. Kennedy and William A. Sunter, entitled Keyed Dead Front Electrical Connector and Cap, and assigned to the same assignee as the present invention now Patent No. 3,233,203, there is disclosed and claimed 'ice a keyed wiring device of the post type. In the embodiment disclosed therein, the shaped key is mounted in the connector socket and extends axially outward through a circular central opening in the spring-loaded socket closure plunger. The key is rotatably mounted relative to the connector. The post of the plug includes a fixed insert which defines the key opening adapted to receive the key. When the connector and plug portions are mated, the key is thus caused to enter the key opening and the plug is then rotated relative to the connector. The rotatable mounting of the key within the connector permits it to turn and the parts are thus interlocked.

Although each of the above-mentioned keyed wiring devices constitutes a significant improvement in wiring devices, and provides decided advantages over the prior art, it also presents certain problems which it would be desirable to correct. These problems arise from the fact that, in order to provide for the interlocking feature of these prior devices, either the key or the insert which defines the key opening must be rotatably mounted in its cap or connector. The requirement that one of these elements be rotatable results in increased difliculty and cost of manufacture, and reduced reliability .and difiiculty in usage. For example, when the key is made rotatable, with normal wear the key eventually becomes somewhat loose in its mounting so that the free end will no longer be accurately centrally positioned. Although this may not be a serious shortcoming under many circumstances, there is at least one class of connectors and plugs in which this condition may create serious problems. These are connectors of the skirted shell type. In one connector of this type, the usual cylindrical protective metallic shell of the connector is flared radially outwardly and spaced from the body adjacent the connecting face. The space thus provided receives the open end of the cylindrical shell of the cap, which is axially extended, i.e. skirted, for this purpose. In this manner, a secure connection and seal is provided between the two wiring device elements. It will be apparent, however, that if the key is not concentric with the skirt, extreme difficulty will be encountered in mating the plug and connector contacts. It is also difficult to connect skirted connectors if the rotatable key means is inadvertently left in an angular position wherein it is not aligned with the stationary key means, because the skirt makes adjustment diflicult.

A major difliculty with wiring devices employing any type of rotatable keying means is that the number of possible different interlocking arrangements is limited substantially to the number of various cross sectional shapes of keys available. These, in turn, are limited by geometrical considerations. In this regard, it should be remembered that only one key configuration should be able to enter any given key opening in keyed connectors of the general type involved if they are to function properly.

Accordingly, it is a primary object of the present invention to provide improved interlocking electrical wiring devices having improved key means wherein the above deficiencies of the prior art are eliminated. Other objects are to provide such wiring devices of either the blade or post type; to provide such wiring devices wherein both the key and the receiving key opening are fixed and nonrotatable; and to provide such wiring devices wherein the number of permitted interlocking relationships is greater than the number of cross sectioned shapes available.

The manner in which the foregoing objects are achieved will be more apparent from the following description, the appended claims and the figures of the attached drawings, wherein:

FIG. 1 is a side elevational view of a post type wiring device embodying the invention comprising a connector and plug aligned to be interconnected with one another, portions thereof being broken away to illustrate the internal construction;

FIG. 2 is a right end elevational View of the connector of FIG. 1;

FIG. 3 is a left end elevational view of the plug of FIG. 1;

FIG. 4 is a cross sectional view taken substantially along the line 44 of FIG. 2, but showing the plug inserted into the connector and rotated to the mated interlocked relationship;

FIG. 5 is a cross sectional view taken substantially along the line 5-5 of FIG. 4;

FIG. 6 is an isometric view of the connector portion of a blade type interlocking wiring device embodying the invention;

FIG. 7 is an isometric view of a plug portion embodying the invention designed to interlock with the connector of FIG. 6;

FIG. 8 is an end elevational view of the connector of FIG. 6;

FIG. 9 is an end elevational view of the plug of FIG. 7;

FIG. 10 is a cross sectional view taken substantially along the line 10-10 of FIG. 8;

FIG. 11 is a cross sectional view taken substantially along the line 1111 of FIG. 9;

FIG. 12 is a longitudinal cross sectional view showing the connector of FIG. 10 and the plug of FIG. 11 in mated interlocked relationship, and

FIG. 13 is a schematic illustration of a plurality of possible keying pin orientations for a single key cross sectional configuration usable in the invention.

As used herein, the term connector is to be construed as including a connector body or any equivalent construction, such as a fixed receptacle, and the term plug as including a connector or attachment plug or cap.

The objects of this invention are achieved in one form by means of a two-element interlocking wiring device wherein: one element includes a front wall defining a fixed shaped key opening; and the other element includes a fixed keying pin having a forward end portion shaped to fit into the key opening to permit mating, but preclude relative rotation, and be slidable through the key opening to a position beyond the rear surface of the front wall when the elements are mated, the shank of the pin being constructed and arranged to then be sufficiently rotatable within the key opening to permit rotational interlocking of the elements of the wiring device.

With particular reference to FIGS. 15, there is illustrated a connector C and a plug P of the post type designed to mate therewith and interlock. The connector C is generally cylindrical and includes a forward body portion 10 of insulating material having an opening therethrough, defining a non-symmetrical cross-sectioned socket 12 formed in part by ribs 14, 16, 18 and 20 projecting into the opening and extending longitudinally thereof. The body portion 10 is also provided with a cavity having peripheral recesses 22, in each of which is disposed an electrical contact 24. The cavity, recesses and socket communicate.

To the rear or inner end of the forward body portion 10 there is secured a central body portion 26 of insulating material. Contacts 24 are supported in portion 26 and extend from its forward side into the recesses 22. An annular disc 28 of insulating material is secured to portion 26, forms the inner wall of the connector C and secures the contacts 24 to portion 26. The indivdual conductors 30, 32 of an electrical cable 34 are connected to the contacts 24 by means of clamping screws 36 in terminal blocks 38. The connector body is enclosed within a cup-shaped cylindrical shell 40 having an inner lining 42 at the rear portion formed of an insulating material that encircles the terminals. The forward portion of shell 40 is circumferentially enlarged and forms a skirt 44 which is spaced radially outwardly from the outer surface of the adjacent part of forward body portion 10. A sliding closure plunger 46 is mounted within the socket 12; it is of a similar non-symmetrical cross section as the socket and includes projecting cars 48, 50, 52 and 54 which extend between and are retained nonrotatable by the ribs of the socket. The outer axial front surface of plunger 46 carries a cross-shaped projection 47. The plunger 46 is normally urged resiliently axially outwardly to close the socket 12 by a coil spring 56, which is mounted between and acts on the front of annular disc 28 and the back of plunger 46. Plunger 46 is formed with stop lugs so it cannot be forced out of the connector C through the socket 12.

The keying function of the invention is performed by means including keying pin 58. The keying pin 58 is centrally fixed to body portion 26 and extends concentrically within the forward body portion 10 outwardly through the center of the coil spring 56 and a central opening 46a formed in plunger 46. Several important features of the keying pin 58 should be noted at this time. One feature is that the pin shank has two different exposed cross sectional shapes. The outer end portion 58a is suitably shaped to mate with a similarly shaped key opening in the plug. In the illustrated embodiment, the cross section of end 58a is triangular. However, it will be apparent that many other cross-sectional shapes may also be employed; for example, the various shapes shown in FIG. 12 of referred-to US. Pat. No. 3,120,985. The shank portion 58b of the keying pin 58 is circular in cross section and of smaller diameter than a circle that falls within the cross section of the outer end portion 58a. The second important feature to note is that the innermost end of the keying pin 58 is firmly embedded, or otherwise fixedly secured, in the central portion 26 of the connector body, thus causing the pin to be fixed and nonrotatable. This end may be ribbed, as shown, or otherwise shaped to securely anchor the pin.

The construction of the plug P will best be understood by reference to FIGS. 1, 3, and 5. From these views it will be seen that the plug comprises a generally cylidrical main body portion 60 constructed of insulating material and a post 62 projecting from the axial forward end of the main body. Post 62 is also of insulating material and generally cylindrical, but of reduced diameter relative to the body portion 60. Post 62 carries on its external peripheral surface a plurality of circumferentially spaced male electrical lug contacts 64 and is of a nonsymmetrical shape similar to socket 12 of the connector C. The contacts 64 are connected in a manner known in the art to the various electrical conductors of electrical cable 66 that is wired to the plug. The post 62 is at least partially hollow and has rigidly mounted in its axial outermost end a nonrotatable plastic, such as nylon, insert 68 which defines a shaped key opening 70 having a configuration (illustrated as triangular) similar to the cross section of the outer end portion 58a of keying pin 58, but being slightly larger so as to readily receive the keying pin therein. The insert 68 thus forms an outer end wall for post 62 having a key opening. The axial outermost ends of the post 62 and insert 68 define a cross-shaped recess 72 for cooperating with the projection 47 on the plunger 46, as taught in the aforementioned Patent No. 2,102,625. The plug body is enclosed within a cylindrical protective metal shell 74 which extends axially forwardly beyond the main body 60 of the plug to form a cylindrical skirt extension about the post 62.

In utilizing the keying means of the invention, the connector C and plug P are aligned as shown in FIG. 1, and the end of the keying pin 58 is advanced into the similarly shaped matching key opening 70 in the plug post insert 68. At approximately the same time, the skirt end of the shell 74 enters the annular space formed between the skirt 44 and the forward body portion 10 of connector C.

As plug P continues to be advanced axially into the connector C, the post 62 contacts and depresses the plunger 46 against the force of spring 56 until the post is inserted axially sufiiciently far to permit the plug P to be rotated. At this point in operation it will be realized that mating of the connector and plug is controlled by the non-symmetrical post 62-socket 12 relationship and the shaped key 58-key opening 70 relationship and, therefore, only a connector and plug meeting both keying requirements can mate. Upon rotation, the lug contacts 64 pass behind, and are retained by, inner surface portions of the forward body portion 10. The cross-shaped projection 47 on the plunger, which is out of alignment with recess 72 initially, enters the recess 72 on the post after full rotation to the interlocked condition. Such locking rotation is possible due to the noval configuration of the keying pin 58 in connector C and the key opening 70 in the insert 68 of plug P. From FIG. 4 it will be noted that the insert 68 is sufiiciently thin for its back surface to clear the shoulder formed between the shaped outer end 58a of the keying pin and its cylindrical shank portion 58b. Thus, when the longitudinal position illustrated in FIG. 4 is reached, the plug P may be rotated, because the cylindrical shank portion 58b of the pin 58 permits the insert 68 to rotate about it without hindrance, which occurs if rotation is attempted when the shaped outer end 58a of the key pin is in the key opening. FIGS. 4 and 5 illustrate the position of the various parts after rotation. It will be noted from the foregoing description that several advantages are achieved by the invention shown in FIGS. 1-5. One of the most obvious advantages, of course, is that the keying pin 58 and the insert 68 are nonrotatably fixed within their respective bodies, thus achieving simplification in manufacture and a rigid structure impossible to secure when one of the keying elements is rotatably mounted as in all known prior art devices. Another important advantage flowing from the fixed mounting of both keying elements is that operation is rendered easy, for the keying pin is not likely to become loose and non-concentric and it cannot be inadvertently misaligned with the key opening, both conditions being possible in the prior art and creating difiicult connection, particularly of skirted connector elements. Still another advantage is that the opening 46a in the plunger 46 may have a close sliding fit with the shaped outer end portion 58a of the keying pin. This creates a better seal than is possible with prior art arrangements in which the opening must be circular, or otherwise enlarged, so that the keying pin may be relatively rotatable therein. Another advantage Will be noted from FIG. 5 wherein it will be seen that an improved locking action is obtained in view of the fact that withdrawal is prevented not only by the lug contacts 64 operating in their usual manner, but also by the misalignment of the cross section of the keying pin outer'end portion 58a with the keying opening 70 in insert 68. p

FIG. 13 helps to illustrate another important advantage of this invention. Wiring devices of this type are polarized so that each contact will engage only its proper counterpart. For example, from FIG. 3 it will be noted that the bottom lug contact 64 is enlarged so that it will enter only the lowermost enlarged portion of the socket 12 shown in FIG. 2. The fundamental purpose of the keying means is to insure that only correspondingly rated elements are mated. If either the pin or the key opening is rotatable the only control over keying resides in the shape of the keying elements, for the potential keying effect of a fixed particular key disposition is nullified. However, when both the pin and its keyWay are fixed, the polarization of the contacts permits the fixed angular disposition of the keying elements to introduce additional keying functions. In FIG. 13, four different key pin dispositions for a fixed triangular key shape are illustrated, which 'should be considered to be correlated with a basically contact polarized connector and plug which permits mating in only one angular relationship of the connector and plug. For example, in FIG. 13a there is illustrated the pin 58 in the position shown in FIGS. 1, 2, 4 and 5. In FIGS. 13b, 0 and d, the same pin is shown rotated by sequential increments from its original position. Each position requires that the key opening in insert 68 be similarly disposed to align with the key pin or the elements cannot be mated. Thus, this single triangular shape produces and is shown in four possible keying dispositions. It will be obvious, of course, that other intermediate positions may also be utilized and that the same technique may be used with other than triangular shapes, for example all those shown in FIG. 12 of Patent No. 3,120,985. The result is that the same or a greater number of differently rated wiring device set-ups may be produced by the invention with a dastically limited number of different cross-sectional shapes for the keying elements, relative to all known prior art devices.

In FIGS. 6-12 there is illustrated a keying arrangement embodying the principle described above incorporated in a different type of connector and plug, namely, the blade type.

FIGS. 6, 8, 10 and 12 illustrate a connector C comprising a front body member 76 of a suitable insulating material and a rear body member 78 also of insulating material secured to and located at one end of the body member 76. These connector body members are enclosed within a protective metallic shell 80, and are all connected together by means of the tie bolts 82 which pass through the members 76, 78 and are threadedly anchored in the end wall of shell 80. The body member 76 is provided with chambers 84 which house female electrical contacts. 86. The contacts 86 are connected to the individual conductors 88 of an electrical cable 90 which are positioned in recesses 92 of body member 78. The forward face of the body member 76 is provided with a plurality of concentric circumferentially spaced arcuate slots 94, each communicating with one of the chambers 84, one slot being shaped to accept a polarizing blade of the plug to allow mating of the connector and plug in only one angular relationship. The body member 76 is provided with a key opening preferably formed by a fixed insert 96 but which can be formed directly in body member 76 as shown in FIG. 1. The insert 96 defines an elongated internal chamber 98 and a key opening 100 which communicates with the face of connector C. Key opening 100 may be shaped as required and, in the illustrated embodiment, is shown as being square. Other shaped key openings, such as those illustrated in Patent No. 3,120,- 985 may be employed and, therefore, inserts with different key openings may be selectively employed.

The plug P, which is connectable with connector C, is illustrated in FIGS. 7, 9, 11 and 12. The plug comprises an insulating body member 102 on which are mounted a plurality of curved concentric blades 104 one of which is configured to be a polarizing blade. The lowermost blade in FIG. 7, and the lowermost slot 94 in FIG. 6 are illustrated as a different shape from the others and function as a basic keying blade-slot to permit connection of the connector and plug in only one way. The blades are widened at their free ends to provide inwardly facing locking shoulders 106 spaced from the outer front surface of the body member 102. The body of the plug P also includes a second insulating body member 108 having therein re cesses 110 for receiving the bared ends of conductors 112 of a cable 114 to permit the conductors 112 to be individually electrically connected to the blades 104. The plug body members 102, 108 are enclosed in a suitable protective metallic shell 116.

Projecting axially outwardly centrally from the body member 102 and at the common center of the blades 104 is a keying pin 118. The keying pin is firmly and nonrotatably secured to the body member 102, and includes a shaped outer end portion 118a and a cylindrical shank portion 11%. The keying pin is similar to that described relative to the preceding embodiment except that the shaped portion 118a has a square, rather than a triangular 7 cross section, so as to fit within the square key opening 100.

To interconnect the plug P and the connector C, the shaped end portion 118a of the keying pin 118 is inserted into the matching key opening 100 and the blades 104 into the corresponding slots 94 The orientation of the connector and plug may be only one relationship because of the keying interaction of both the keying slot-blade and the keying pin and key opening. The plug and connector are advanced together until the locking shoulders 106 are completely within the chambers 84, and at that time the shaped outer end portion 118a of the keying pin has passed completely through the key opening. At this point, the plug P may be rotated relative to the connector C until the locking shoulders 106 lock against the inner surface of the front wall of the chambers 84. During this rotation, the reduced diameter cylindrical shank portion 118b of the keying pin is free to rotate within the key opening. After rotation, the members are disposed as shown in FIG. 12. Although the shells 80 and 116 are illustrated as not extending beyond the front faces of the connector and plug, they may be formed as in FIGS. 1-5 embodiment.

It will be apparent that the advantages of simplified construction and operation, reliability and ease of use, improved locking and increased versatility, which have been previously described in relation to the embodiment of FIGS. 1-5 are equally produced by the embodiment of FIGS. 6-12.

It will be apparent to those skilled in the art that all the objectives set forth above are achieved by the present invention. It will also be apparent that a number of variations and modifications may be made in this invention without departing from the spirit and scope. Accordingly, the foregoing is to be construed as illustrative only, rather than limiting. This invention is limited only by the scope of the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a rotational locking multi-wire electrical connector and plug having cooperating electrical contacts arranged to engage on mating of the connector and plug and means for interlocking on relative rotation of the connector and plug after the contacts have engaged, the improvement which comprises: one of said connector and plug defining a cavity therein at least partially bounded by a front wall, said front wall defining a noncircular key opening of fixed relative orientation communicating with said cavity; and the other of said connector and plug having mounted thereon a fixed projecting keying pin arranged to enter said key opening on the mating of said connector and plug, said keying pin having an outer end portion disposed to initially enter said key opening and said outer end portion having a noncircular cross sectional configuration similar to that of said key opening to pass therethrough in a fixed angular relationship and enter said cavity, said keying pin having a shank portion adjacent said outer end portion disposed to enter said key opening thereafter and of a configuration and disposition to be rotatable in said key opening and of a length sufficient to displace said outer end portion entirely out of said key opening when said connector and plug are fully mated to permit their relative rotation.

2. The improvement of claim 1 wherein said shank portion is concentric with the axis of relative rotation of said connector and plug.

3. The improvement of claim 1 wherein at least one radial dimension of said outer end portion measured from the axis of relative rotation between said connector and plug is greater than the radial dimension of said shank portion.

4. The improvement of claim 1 wherein at least one of said connector or plug includes a protective shell having a skirt projecting beyond its front to encircle a part of the other when they are mated.

5. The improvement of claim 1 wherein said connector defines a socket leading to its electrical contacts and said plug includes a post carrying electrical contacts and insertable into said socket; said front wall defines at least a portion of the mating end of said post; and said keying pin is mounted in said socket.

6. The improvement of claim 5 wherein said connector includes plunger means resiliently mounted in said socket to normally close it; said plunger means defining an opening therethrough arranged to slidably receive and enclose said pin.

7. The improvement of claim 6 wherein the opening in said plunger is similar in shape to the cross section of the outer end portion of said keying pin.

8. The improvement of claim 1 wherein said connector includes said front wall and defines said cavity; said front wall further defines a plurality of arcuate slots concentric with said key opening; and said plug includes said keying pin and a plurality of curved blades concentric relative to said pin and positioned to enter said slots when said key opening and keying pin mate.

9. The improvement of claim 1 wherein the electrical contacts of said connector and plug are arranged to permit initial mating in only one relative angular disposition of the connector and plug.

10. A rotational locking multi-wire electrical wiring device which comprises: a connector body of insulating material defining a recess therein and including an end Wall defining a socket communicating with said recess; a plurality of first electrical contact means mounted within said recess; a fixed keying pin mounted within said recess extending outwardly of said connector body and through said socket, said keying pin having a noncircular outer end portion and a shank portion, at least one radial dimension of said outer end portion being greater than the radial dimension of said shank portion; plunger means reciprocatingly mounted within said socket for depression into said recess, said plunger means defining an opening of a shape for receiving said keying pin; spring means Within said recess resiliently urging said plunger means outwardly and into said socket to form a closure therefor; a plug body of insulating material; a post extending from said plug body having second electrical contact means mounted thereon and dimensioned to be inserted within said socket; said post defining a cavity therein; and an end wall on said post defining a fixed key opening communicating with said cavity, said key opening having a noncircular configuration similar to the cross sectional configuration of the outer end portion of said keying pin, said end wall being of a thickness to permit the shank portion of said keying pin to be encircled thereby when said post is inserted into said socket a distance sufiicient to permit engagement of said first and second electrical contact means.

11. A rotational locking multi-wire electrical wiring device which comprises: a connector body of insulating material defining a plurality of circumferentially positioned chambers therein and a central cavity; an end wall on said connector body defining a plurality of concentric arcuate slots, each communicating with one of said chambers, and a central noncircular, fixed key opening communicating with said cavity; a plurality of electrical contact means disposed within said chambers; a plug body of insulating material; a plurality of concentrically arranged curved contact blades extending from said plug body and arranged to enter said arcuate slots; and a fixed keying pin on said plug body extending outwardly therefrom and concentric within said blades, said keying pin having an outer end portion and a shank portion, said outer end portion having a noncircular cross sectional configuration similar to the configuration of said key opening, at least one radial dimension of said outer end portion being greater than the radial dimension of said shank portion, said shank portion having a length sufficient to displace said outer end portion completely out of said key opening upon insertion of said blades into said slots and into engagement with said electrical contact means.

12. A connector for a rotational locking multi-wire electrical wiring device which comprises: a connector body of insulating material defining a recess therein and including an end wall defining a socket communicating with said recess; a plurality of electrical contact means mounted within said recess; a fixed keying pin mounted within said recess extending outwardly of said connector body and through said socket, said keying pin having a noncircular outer end portion and a shank portion, at least one radial dimension of said outer end portion being greater than the maximum radial dimension of said shank portion; plunger means reciprocatingly mounted Within said socket for depression into said recess, said plunger means defining an opening receiving said keying pin; and spring means within said recess resiliently urging said plunger means outwardly and into said socket to form a closure therefor.

13. A plug for rotational multi-wire electrical wiring device which comprises: a plug body of insulating material; a plurality of concentrically arranged curved contact blades extending from said plug body; and a fixed keying pin on said plug body extending outwardly therefrom and concentric Within said blades, said keying pin having a noncircular outer end portion and a shank portion, at least one radial dimension of said outer end portion being greater than the maximum radial dimension of said shank portion.

14. A multi-wire connector and plug: said connector comprising an insulating body housing electrical contacts; said plug comprising an insulating body housing electrical contacts disposed for engagement with the contacts of said connector on mating of the connector and plug which is permitted to occur in only one relative angular disposition; interlocking means to prevent separation of the plug and connector mounted to become effective and ineifective by relative turning movement between the plug and connector; said interlocking means being arranged to become effective by relative turning movement between the connector and plug only after the contacts are in engagement; and keying means comprising a fixed, noncircular key opening in one of said connector and plug and a fixed key pin on the other, said key pin and opening being configured and disposed to permit initial insertion of said key into said key opening but no relative rotation of said connector and plug, and thereafter to permit such relative rotation.

References Cited UNITED STATES PATENTS 1,996,410 4/ 1935 Edwards 339--206 2,617,166 11/ 1-952 Kaufmann 24--211 2,871,456 1/1959 Healy 339-42 3,120,985 2/1964 Hubbell 33931 3,233,203 2/1966 Kennedy et al. 33942 MARVIN A. CHAMPION, Primary Examiner.

EDWARD C. ALLEN, Examiner.

I. H. MCGLYNN, Asssitant Examiner. 

1. IN A ROTATIONAL LOCKING MULTI-WIRE ELECTRICAL CONNECTOR AND PLUG HAVING COOPERATING ELECTRICAL CONTACTS ARRANGED TO ENGAGE ON MATING OF THE CONNECTOR AND PLUG AND MEANS FOR INTERLOCKING ON RELATIVE ROTATION OF THE CONNECTOR AND PLUG AFTER THE CONTACTS HAVE ENGAGED, THE IMPROVEMENT WHICH COMPRISES: ONE OF SAID CONNECTOR AND PLUG DEFINING A CAVITY THEREIN AT LEAST PARTIALLY BOUNDED BY A FRONT WALL, SAID FRONT WALL DEFINING A NONCIRCULAR KEY OPENING OF FIXED RELATIVE ORIENTATION COMMUNICATING WITH SAID CAVITY; AND THE OTHER OF SAID CONNECTOR AND PLUG HAVING MOUNTED THEREON A FIXED PROJECTING KEYING PIN ARRANGED TO ENTER SAID KEY OPENING ON THE MATING OF SAID CONNECTOR AND PLUG, SAID KEYING PIN HAVING AN OUTER END PORTION DISPOSED TO INITIALLY ENTER SAID KEY OPENING AND SAID OUTER END PORTION HAVING A NONCIRCULAR CROSS SECTIONAL CONFIGURATION SIMILAR TO THAT OF SAID KEY OPENING TO PASS THERETHROUGH IN A FIXED ANGULAR RELATIONSHIP AND ENTER SAID CAVITY, SAID KEYING PIN HAVIGN A SHANK PORTION ADJACENT SAID OUTER END PORTION DISPOSED TO ENTER SAID KEY OPENING THREAFTER AND OF A CONFIGURATION AND DISPOSITION TO BE ROTATABLE IN SAID KEY OPENING AND OF A LENGTH SUFFICIENT TO DISPLACE SAID OUTER END PORTION ENTIRELY OUT OF SAID KEY OPENING WHEN SAID CONNECTOR AND PLUG ARE FULLY MATED TO PERMIT THEIR RELATIVE ROTATION. 